The lung is constantly exposed to biological toxins including lipopolysaccharide (LPS or endotoxin) that activate Toll-like receptor (TLR) signaling, thereby inducing potentially injurious inflammation that can contribute to many diseases including COPD, allergy, and cancer. While these environmental agents are ubiquitous in the environment, unless the exposures are severe or there is some underlying condition, they don't in general induce disease. This suggests the existence of a dampening mechanism(s) that prevents inflammation. One such mechanism is the production of negatively acting alternative mRNA splice forms in the TLR signaling pathway. Prolonged environmental exposure to LPS induces the production of these negatively acting splice forms. Thus we hypothesize a generalized dampening system for TLR signaling in the lung that involves alternative pre-mRNA splicing to generate inhibitory molecules that limit the extent of pro-inflammatory responses induced by LPS. Despite the identification of many negatively acting alternative splicing events in the TLR signaling pathway, there has been no mechanistic study of how this alternative splicing is regulated or how to best utilize this information to treat LPS-induced disease. Our preliminary studies have now identified two factors that modulate alternative splicing in the TLR signaling pathway. One factor is components of the core splicing machinery including the SF3a complex, which functions with the rest of the spliceosome to control mRNA splicing. Surprisingly, there is substantial specificity of SF3a for alternative splicing in the TLR signalin pathway. The other factor is components of the TLR signaling pathway itself. The overall goal of this proposal is to investigate the mechanistic relationship between LPS exposure, TLR signaling, and alternative pre-mRNA splicing in the TLR pathway. To achieve this goal, we propose to investigate (1) how the TLR signaling pathway mediates the effects of LPS on alternative mRNA splicing, (2) how SF3a and the core spliceosome mediates the effects of LPS on alternative mRNA splicing, and (3) how the TLR signaling pathway and core splicing machinery interact to affect LPS- induced alternative splicing. These mechanistic studies will pave the way for harnessing this negative feedback loop to treat LPS-induced inflammatory disease.